In recent years, a wearable type image display device such as a head mounted display has attracted attention. As such a head mounted display, a see-through type device with which it is possible to visually recognize both a video (virtual image) from a display element and an image (external light) of outdoor scenes at the same time has been known (for example, refer to PTL 1).
In such a see-through type image display device, even if a wearer having a near-sightedness, long-sightedness, or the like, visibility of the external light is increased by performing diopter adjustment of the external light.